EP1047812A2 - Anodic electrophoretic coating method - Google Patents

Abstract

A method for anodic electro-dip lacquer coating, wherein coating medium which is consumed in an anodic electro-dip bath is compensated for by an under-neutralised anodic replenishment material, wherein the replenishment material comprisesA) a pigment-free aqueous binder vehicle component with a solids content of 40 to 70% by weight, an MEQ value of 15 to 40 and a content of organic solvent of <=0.5% by weight, andB) a pigment-containing aqueous paste resin component with a solids content of 60 to 75% by weight, an MEQ value of 5 to 15 and a content of organic solvent of <=1.0 % by weight,wherein A) and B) are present in a ratio by weight of 1:1 to 4:1 and the mixture of A) and B) has a solids content of 45 to 73% by weight, a solvent content of <=0.75% by weight and an MEQ value which is 50 to 70% lower than the MEQ value of the electro-dip bath.

Description

Process for anodic electrocoating

The present invention relates to a method for producing an anodic electrodeposition coating (ATL) using a low-solvent / free electrodeposition coating bath (ATL bath), wherein electrodialysis in the ETL bath is not required to maintain the bath and coating parameters. It is also not necessary to regularly discard ultrafiltrate.

The principle of anodic electrocoating (ATL) is described in the literature and has become established in practice. Even after the introduction of cathodic electrocoating (KTL), anodic electrocoating is still a widespread coating process, especially for coating industrial goods. On the one hand, this is due to the large number of anodic coating systems available, and on the other hand on the good level of today's anodic coating materials. Certain materials, such as Aluminum to be coated more advantageously with anodic than with cathodic electrocoating compositions. With the anodic

Electrodeposition coating is used to bring a workpiece with an electrically conductive surface made of metal or from electrically conductive plastic or from a substrate provided with an electrically conductive coating into an aqueous ATL bath and connected as an anode to a direct current source.

The ATL bath consists of an aqueous dispersion, e.g. Suspension or emulsion or from an aqueous solution of one or more binders which have been made at least partially water-dispersible or water-soluble by salt formation with organic or inorganic neutralizing agents, from pigments, fillers, additives and other auxiliaries dispersed therein.

When an electrical direct current is applied, the polymer particles of the aqueous dispersion of the ATL bath migrate to the anode and react there with those of the At the same time, water electrolysis takes place to form the water-insoluble polymer, which coagulates from the aqueous phase and deposits on the anode as a lacquer film with the additives dispersed therein. (Metallfläche 31 (1977) 10, pp. 455 to 459).

The usual ATL baths are operated continuously, i.e. The substrates described above are immersed and coated in an electrodeposition basin filled with the coating agent. This removes solid matter from the ATL bath and at the same time releases neutralizing agent in the ATL bath. In order to keep the coating parameters and the quality of the coating constant, it is necessary to add refill material with an increased solid content to the ATL bath to compensate for the extracted solid and to compensate for the neutralizing agent released in the ATL bath to maintain the desired MEQ value.

There are basically two compensation methods for compensating for the solid body extracted from the ATL bath and the neutralizing agent released. The supplied refill material with an increased solid content is neutralized less than the ATL bath, and the released neutralizing agent is required to disperse / homogenize the refill material in the ATL bath and is consumed in the process. The compensation can also be done with fully neutralized refill material. The expenditure on equipment is then greater, however, since the released neutralizing agent has to be removed by means of (electro) dialysis (Glasurit Manual 1984, page 377 and Willibald Machu "Electrocoating", Verlag Chemie GmbH Weinheim / Bergstrasse, 1974, page 166). The neutralizing agent released during the coating can also be removed by regularly discarding ultrafluidate.

When the neutralizing agent released during the coating is compensated by less neutralized refill material, this requires a high content of up to about 15% by weight of organic solvents, since it is otherwise unstable and too highly viscous and does not penetrate into the coating material, which can contain up to 90% May contain water, can be incorporated. Coating agents of this type are described, for example, in DE-A-32 47 756.

In paint and varnish 103, year 6/97, page 26, a new environmentally friendly anodic one-component system (IC system) for the

Electro-dip coating, which still contains 6% organic solvent in the refill paste form and 0.5% in the running bath.

However, high levels of solvents are undesirable because of the pollution of the exhaust air and wastewater, whereby the legal regulations require the entire use of materials

Use calculations as a basis. To remove the neutralizing agent released during the coating, the cathodes can also be placed in the ATL bath in washable dialysis cells (electrodialysis) and the neutralizing agent obtained there discarded, or the coating material can be subjected to ultrafiltration continuously or discontinuously and the ultrafiltrate obtained at least partially at regular intervals discard. Because of the higher investment costs and a higher maintenance and monitoring effort, such electrodialysis devices are not available in most ATL baths. The regular discarding of ultrafiltrate or dialysate also requires more effort in the treatment of water and is therefore undesirable.

The compensation of electro-dip coating baths with fully neutralized material, consisting of one or two components, is known from the literature (Glasurit manual 1984, page 377) and is described there using the example of cathodic electro-dip coating. However, as already mentioned, the use of electrodialysis and the rejection of dialysate is absolutely necessary.

The object was therefore to provide a process for the preparation of an aqueous, low-solvent or solvent-free coating composition for anodic electrocoating, when used to coat conductive substrates in an ATL bath to maintain the

Bath and coating parameters do not mean removal of the neutralizing agent released during coating by an electrodialysis device is required and a large amount of ultrafiltrate does not have to be regularly discarded.

Surprisingly, this object has been achieved in that an anodic refill material, consisting of a pigment-free aqueous binder component and a pigment-containing aqueous paste resin component, is used to compensate for the coating material used in the electro-dip coating and the neutralizing agent released, which is so low that it is under-neutralized so that when it is added to the ATL bath compensates the neutralizing agent released there and still contains only small amounts of organic solvents.

The invention therefore relates to a process for anodic electrodeposition in which the coating agent used in an anodic electrodeposition bath is compensated for by a neutralized anodic refill material, which is characterized in that the refill material consists of

A) a pigment-free aqueous chemical component with a solids content of 40 to 70 wt .-%, an MEQ value of 15 to 40 and an organic solvent content of <0.5 wt .-% and

B) there is a pigment-containing aqueous paste resin component with a solids content of 60 to 75% by weight, an MEQ value of 5 to 15 and an organic solvent content of <1.0% by weight,

wherein A) to B) are present in a weight ratio of 1: 1 to 4: 1 and the mixture of A) and B) has a solids content of 45 to 73% by weight, a solvent content of <0.75% by weight and one MEQ value that is 50 to 70% lower than the MEQ value of the electro-dip.

The solids content of components A) and B) can, for example, according to DIN EN

ISO 3251 at 30 '180 ° C. The solids content of component A) is preferably 45 to 65% by weight. The solids content of component B) is preferably 60 to 73% by weight.

The MEQ value of component A) is preferably 20 to 35, the MEQ value of component B) is preferably 5 to 10. The MEQ value is a measure of the content of neutralizing agent in a water-based paint. It is defined as the amount of milliequivalents of the neutralizing agent based on 100 g solids.

The organic solvent content of component A) is preferably <0.4% by weight, that of component B) is preferably <0.5% by weight.

The mixing ratio of component (A) to component (B) is 1: 1 to 4: 1, preferably from 2: 1 to 3.5: 1, based on the weight of the respective aqueous component.

The mixture has a solids content of 45 to 73 wt .-%, a

Solvent content of at most 0.75% by weight and an MEQ value which is 50 to 70%, preferably 60 to 70% lower than the MEQ value of the ATL bath in the coatable state.

Component (A) contains the binder or binders of the aqueous coating agent, and optionally a biocidal component and, if necessary, crosslinking agents and, if appropriate, emulsifiers, layering agents, further additives such as e.g. Neutral resins, common paint additives such as light stabilizers and optical brighteners.

Component (B) contains one or more paste resin (s), pigments and / or fillers, if appropriate a biocidal component and, if necessary, crosslinking agents, and if appropriate layering agents and customary paint additives and further additives, for example as they are also present in component (A) can.

All binder systems can be used as suitable binders of component (A) an acid number from 20 to 150, preferably from 20 to 120 and a hydroxyl number from 20 to 150, preferably from 60 to 120, such as are known for aqueous coating systems, especially for anodic electrocoat coatings.

These include, for example, polyester, polyacrylate and polyurethane resins; modified polyester or polyurethane resins, e.g. Alkyd resins, urethanized polyester resins or acrylated polyester or polyurethane resins, as well as mixtures of these resins. Polyester resins are preferred.

Suitable polyester resins in component (A) are, for example, carboxyl-containing and hydroxyl-containing polyesters having an acid number of 20 to 150 and a hydroxyl number of 20 to 150. They are obtained by the processes known to the person skilled in the art by reacting polyhydric alcohols and polyhydric carboxylic acids or carboxylic acid anhydrides, and optionally aromatic and / or aliphatic monocarboxylic acids. The required hydroxyl group content is set in a manner known per se by suitable choice of the type and proportions of the starting components. The carboxyl groups can be introduced, for example, by half-ester formation from a prefabricated, hydroxyl-containing polyester resin with acid anhydrides. Carboxyl groups can also be incorporated, for example, by using hydroxycarboxylic acids in the polycondensation reaction.

The dicarboxylic acids and the polyols can be aliphatic or aromatic

Be dicarboxylic acids and polyols.

The low molecular weight polyols used to produce the polyesters are, for example, diols such as alkylene glycols, for example ethylene glycol, butylene glycol, hexanediol, hydrogenated bisphenol A and 2,2-butylethyl propanediol, neopentyl glycol and / or other glycols such as dimethylolcyclohexane. However, higher functional or mixtures of higher and monofunctional OH components such as tri- methylolpropane, pentaerythritol, glycerin, hexanetriol; Polyethers that are condensates of glycols with alkylene oxides; Monoethers of such glycols, such as diethylene glycol monoethyl ether, tripropylene glycol onomethyl ether, are used.

The acid component of the polyester preferably consists of low molecular weight

Dicarboxylic acids or their anhydrides with 2 to 18 carbon atoms in the molecule.

Suitable acids are, for example, phthalic acid, isophthalic acid, terephthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid, adipic acid, azeleic acid, sebacic acid, fumaric acid, maleic acid, glutaric acid, succinic acid, itaconic acid and / or

1,4-cyclohexanedicarboxylic acid. Instead of these acids, their methyl esters or anhydrides, if they exist, can also be used. In order to obtain branched polyesters, it is also possible to add proportions of higher-functional carboxylic acids, such as trifunctional carboxylic acids, trimellitic acid, malic acid, aconitic acid, bishydroxyethyl taurine and dimethylolpropionic acid, dimethylolbutyric acid or bisanhydrides. Polycarboxylic acids that do not form cyclic anhydrides are preferred.

The polyester resins can, for example, also by incorporating unsaturated compounds, compounds containing isocyanate groups or by lap or

Graft polymerization can be modified with ethylenically unsaturated compounds.

Preferred polyesters in component (A) are, for example, carboxyl-containing polyesters with an acid number from 20 to 120, a hydroxyl number from 20 to 150, preferably from 60 to 120. They are for example

Reaction products from two and / or polyhydric aliphatic or cycloaliphatic saturated alcohols, aliphatic, cycloaliphatic and / or monocyclic aromatic dibasic or polybasic polycarboxylic acids and optionally linear or branched, saturated or unsaturated aliphatic and / or cyclialiphatic C - to C2Q-monoalcohols or monoalcohols.

The quantitative ratios of the starting components are calculated from the molar ratios to the desired acid numbers and hydroxyl numbers of the Lead resin. The selection of the individual starting components is known to the person skilled in the art, taking into account the objective.

The number average molecular weight Mn, measured against polystyrene as calibration substance, is for example 1000 to 6000, preferably 2000 to 4000.

Oil-free polyesters containing carboxyl groups, such as those e.g. are described in DE-A-32 47 756.

These polyesters preferably contain 0.3 to 3.0, particularly preferably 0.5 to 2.5 milliequivalents of aliphatic, cycloaliphatic and / or monocyclic aromatic

Dicarboxylic acids condensed per gram of resin. Of tri- or polybasic cyclic carboxylic acids, 0.8 to 2.0, preferably 0.9 to 1.8, particularly preferably 1.1 to 1.5 millimoles per gram of resin are expediently bound to the polyester via only one carboxyl group. Three- and / or polybasic polycarboxylic acids are used as polycarboxylic acids, preferably three- and / or four-basic acids. These polyesters are produced in a manner known per se by polycondensation of the starting materials, preference being given to working in stages to avoid clouding and gel formation.

The esterification of preferably aromatic and cycloaliphatic dicarboxylic acids, which cannot form an intramolecular anhydride, is preferably carried out with dialcohols which either contain secondary OH groups or contain sterically hindered primary OH groups by substitution with JS, an OH group-containing polyester being formed by excess alcohol. The alcohols preferably contain 2 to 21, particularly preferably 4 to 8 carbon atoms. The dicarboxylic acids preferably contain 5 to 10 carbon atoms, particularly preferably 6 carbon atoms.

Examples include isophthalic acid, terephthalic acid, 1,3- and 1,4-cyclohexanedicarboxylic acid or alkyl-substituted dicarboxylic acids

Butyl isophthalic acid. Isophthalic acid is particularly preferred. To achieve branching, a corresponding one can be used instead of some of the dicarboxylic acids Amount of tricarboxylic acid such as trimellitic anhydride can be condensed into the resin molecule. On the other hand, dimethyl esters such as dimethyl terephthalate or dimethyl 1,4-cyclohexanedicarboxylate can also be introduced into the polyester by transesterification, if appropriate in the presence of transesterification catalysts.

Preferred dialcohols are neopentyl glycol, hydroxypivalic acid neopentyl glycol ester, hexanediol-2,5, 1,4-bis (hydroxymethyl) cyclohexane, 1 J-isopyrilidine-bis- (p-phenoxy) -2-propanol, 2,2,4-trimethylpentanediol. 1,3, as well as mixtures thereof.

The glycidyl ester of α-branched fatty acids, such as versatic acid, can also be used as dialcohol, for example, because the fatty acid is incorporated into the molecule in a manner which is stable to hydrolysis. In special cases it is also possible to use epoxy resins whose epoxy groups have been reacted with monoalcohols.

A partial use of polyols with more than two OH groups such as trimethylolpropane or pentaerythritol is possible to set suitable OH numbers and viscosities. The same applies to a minor modification to

Elastification with long-chain dialcohols such as 1,6-hexanediol or aliphatic dicarboxylic acids such as adipic acid.

This esterification (first stage) is carried out azeotropically in a known manner or in the melt at elevated temperature (above 190 ° C.) and gives a clear result

Product with an acid number from 0 to 50, preferably from 5 to 25 and a viscosity of 200 to 3000 mPas at 25 ° C., measured in a 75% butyl glycol solution.

To enable solubility in the aqueous alkaline medium, carboxyl groups must also be introduced into the OH group-containing polyesters. For this purpose, a reaction takes place at temperatures below 190 ° C. with an aromatic or cycloaliphatic dicarboxylic acid, which is preferably carried out by defunctionalization a long-chain, aliphatic hydrophobic monoalcohol from a polycarboxylic acid with three or four carboxyl groups such as trimesic acid, hemellitic acid, pragmatic acid and mellophanic acid. The process is particularly simple when using anhydride-containing compounds such as trimellitic anhydride, pyromellitic anhydride or corresponding hydrogenated ring systems, and also cyclopentanetetracarboxylic anhydride or pyrazine tetracarboxylic anhydride.

The polycarboxylic acids can, for example, be reacted stoichiometrically with so much monoalcohol in a two-pot process that a dicarboxylic acid is retained, which is then added to the OH group-containing polyester at temperatures of about 150 to 190 ° C.

In practice, the production of the carboxyl group-containing polyesters in a one-pot process has proven itself by adding the OH group-containing polyester to the first

Step the approximately stoichiometric amounts of monoalcohol and trimellitic anhydride are added in the order given.

Straight-chain and / or branched saturated and / or unsaturated, primary, secondary and / or tertiary, preferably primary and / or secondary alcohols can, for example, be used as monoalcohols. Mixtures, in particular isomeric mixtures, of these alcohols can also be used. Aliphatic C6 to C18 monoalcohols and benzyl alcohol and its alkyl substitution products are preferred. Branched-chain C8 to C13 iso-monoalcohols are particularly preferred. Particularly half-esters that are stable to hydrolysis are produced by

Obtain use of cu-branched monoalcohols or secondary monoalcohols such as cyclohexanol or secondary methyl octyl alcohol. The structure of the resin ensures that any fission products (monoalcohol and trimellitic acid monoesters) which may be formed by hydrolysis are deposited electrophoretically with the film without interference.

The incorporation of carboxyl groups can also, for example, by using Hydroxycarboxylic acids such as dimethylolpropionic acid take place in the polycondensation reaction, the free carboxyl group of which generally does not participate in the polycondensation reaction because of the steric hindrance, so that this acid is incorporated exclusively via the hydroxyl groups.

The molar ratios of the overall formulation for the production of the polyester are chosen so that a viscosity suitable for the respective application is achieved. It is, for example, about 200 to 3000, preferably 250 to 2000 and particularly preferably 300 to 1500 mPas, measured 50% in butyl glycol at 25 ° C. Like the molecular weight, it can be adjusted by mixing resins with higher and lower viscosity, or higher and lower molecular weight. The upper limit of the acid number is preferably below 100, particularly preferably below 60; the lower limit of the acid number is preferably above 35, particularly preferably above 40. The carboxyl-containing polyester contains at least one, preferably at least two, carboxyl groups per molecule, by which

To achieve water solubility by salt formation with a low molecular base. If the acid number is too low, the solubility is too low; if it is too high, the high neutralization causes an increased electrolysis in the ATL bath, which can lead to surface defects. The selected excess of alcohol gives a hydroxyl number of about 20 to 150, preferably from 60 to 120, in the finished resin

Resins preferred which have a relatively high hydroxyl number with a low acid number.

The polycondensation takes place, for example, azeotropically or in the melt, for example at reaction temperatures between 160 to 240 ° C., preferably between 160 to 210 ° C. After reaching the desired final resin values with regard to viscosity and acid number, the mixture is cooled to a temperature such that a product with a viscosity is obtained which ensures that water is incorporated. In practice, this means that the melt viscosity achieved should not exceed 40,000 mPa.s. This can be achieved by cooling to a suitable temperature.

Unless you are working under pressure, this is up to about 100 ° C. The polycondensation product is neutralized for transfer into an aqueous solution or dispersion. For this purpose, the neutralizing agent can be added to the polycondensation resin before or during the addition of water, but it can also be placed in the water in which the polycondensation resin is dispersed. For example, high-speed stirring disc devices,

Rotor / stator mixers or high pressure homogenizers are used. During or after the transfer into the aqueous solution or dispersion, organic solvents can optionally be removed by distillation.

Suitable bases, such as ammonia, are suitable as neutralizing agents for this purpose; primary, secondary and tertiary amines such as diethylamine, triethylamine, morpholine; Alkanolamines such as diisopropanolamine, dimethylaminoethanol, triisopropanolamine, dimethylamino-2-methylpropanol; quaternary ammonium hydroxides or optionally also small amounts of alkylene polyamines such as ethylenediamine. Mixtures of these can also be used

Neutralizing agents can be used.

The stability of the aqueous dispersion can be influenced by the choice of the neutralizing agent. The amount of neutralizing agent is chosen so that the MEQ value of the mixture of component (A) and component (B) is 50 to 70% below the MEQ value of the ATL bath.

Suitable polyacrylate resins in component (A) are, for example, copolymers containing carboxyl groups and / or sulfonic acid groups with an acid number of 20 to 150 and a number-average molecular weight Mn of 1,000 to 10,000.

They are produced by customary processes by copolymerization of olefinically unsaturated monomers, monomers containing acid groups being copolymerized with further monomers. The monomers containing acid groups are also used for the purpose of incorporating carboxyl and / or sulfonic acid groups into the copolymers, which, owing to their hydrophilicity, have the effect of Ensure water solubility or water dispersibility of the copolymers, especially after the at least partial neutralization of the acid groups.

Suitable monomers containing acid groups are in principle all olefinically unsaturated polymerizable compounds which have at least one carboxyl and / or sulfone group, such as, for example, olefinically unsaturated mono- or dicarboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, fumaric acid, maleic acid, itaconic acid or the half esters of fumaric acid, Maleic acid and itaconic acid or olefinically unsaturated compounds containing sulfonic acid groups, such as, for example, 2-acrylamido-2-methylpropanesulfonic acid or any mixtures of such olefinically unsaturated acids. Acrylic acid and methacrylic acid are particularly preferred.

In order to achieve the desired application properties in the finished lacquer, the copolymers may contain, in addition to the monomers containing acid groups, further functional monomers with which e.g. Have cross-linking reactions carried out. Both self-crosslinking of the copolymers and external crosslinking with other components additionally incorporated into the lacquer can take place.

Examples of such functional groups are hydroxyl, amino, amido, keto, aldehyde, lactam, lactone, isocyanate, epoxy and silane groups. Olefinically unsaturated monomers which carry such functional groupings are known. Hydroxy and epoxy groups are particularly preferred. Furthermore, in principle, all non-functional olefinically unsaturated monomers can be used in the preparation of the copolymers.

Suitable non-functional monomers are, for example, esters of acrylic and methacrylic acid, the alcohol components of which contain 1 to 18 carbon atoms, vinyl aromatics, vinyl esters of aliphatic monocarboxylic acids, acrylic and

Methacrylonitrile. The copolymers can be prepared by polymerization using customary processes. The copolymers are preferably prepared in organic solution. Continuous or discontinuous polymerization processes are possible.

Aromatics, esters, ethers and ketones can be used as solvents. Glycol ethers are preferably used.

The copolymerization is generally carried out at temperatures between 80 to 180 ° C using conventional initiators such as aliphatic

Azo compounds or peroxides. Conventional regulators can be used to regulate the molecular weight of the polymers. After the polymerization has ended, the copolymers, as described for the polycondensation resins, can be neutralized and converted into an aqueous solution or dispersion, the organic solvent optionally being able to be removed by distillation.

Suitable polyurethane resins in component (A) are, for example, anionic polyurethane resins which contain carboxyl, sulfonic acid and / or phosphonic acid groups in salt form. They are produced in a manner known per se from polyols, polyisocyanates and optionally chain extenders.

The polyurethane resins can be produced both in bulk and in organic solvents which cannot react with isocyanates. As described for the polycondensation resins, they are converted into the aqueous phase by neutralizing the acid groups. In many cases, it is useful to

To produce polyurethane resins in stages.

For example, it is possible first to prepare a prepolymer with acid groups and terminal isocyanate groups in organic solvents, which, after neutralization of the acid groups with tertiary amines, is chain-extended and transferred into the aqueous phase, the organic solvents being able to be removed by distillation. The polyols used to prepare the prepolymer can be low and / or high molecular weight and can also contain anionic groups.

Low molecular weight polyols preferably have a number average molecular weight Mn of 60 to 400 and can contain aliphatic, alicyclic or aromatic groups. You can use up to 30 wt .-% of the total polyol components.

Suitable low molecular weight polyols are, for example, diols, triols and polyols, such as ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propanediol, 1,3-

Propanediol, 1,4-butanediol, 1,2-butylene glycol, 1,6-hexanediol, trimethylolpropane, castor oil or hydrogenated castor oil, pentaerythritol, 1,2-cyclohexanediol, 1,4-cyclohexanedimethanol, bisphenol A, bisphenol F, neopentyl glycol, hydroxypivalic acid neopentyl glycol ester , hydroxyethylated bisphenol A, hydrogenated bisphenol A and mixtures of these polyols.

High molecular weight polyols consist of linear or branched polyols with an OH number of 30 to 150. You can use up to 97 wt .-% of the total polyol components. These are preferably saturated or unsaturated polyester and / or polyether diols and / or polycarbonate diols with a molecular weight Mn of 400 to 5000 or mixtures thereof.

Suitable linear or branched polyether diols are, for example, poly (oxyethylene) glycols, poly (oxypropylene) glycols and / or poly (oxybutylene) glycols.

Polyesters are preferred and are prepared in a known manner by esterification of dicarboxylic acids or their anhydrides with diols. To produce branched polyesters, polyols or polycarboxylic acids with a higher functionality can also be used to a small extent.

The groups capable of forming anions can originate from the polyester or they are introduced into the prepolymer by using compounds which contain two H-active groups which react with isocyanate groups and at least one group which is capable of forming anions. Suitable groups which react with isocyanate groups are, in particular, hydroxyl groups and primary and / or secondary amino groups. Groups which are capable of forming anions are, for example, carboxyl, sulfonic acid and / or phosphonic acid groups. Examples of such compounds are dihydroxycarboxylic acids such as dihydroxypropionic acid, dihydroxybutyric acid, dihydroxysuccinic acid, diaminobenzoic acid and preferably α, α-dimethylolalkanoic acid such as dimethylolpropionic acid.

Suitable polyisocyanates are aliphatic, cycloaliphatic and / or aromatic polyisocyanates with at least two isocyanate groups per molecule and the known biuret, AUophanat, urethane and / or isocyanurate group derivatives of these diisocyanates and mixtures of these polyisocyanates. The isomers or isomer mixtures of organic diisocyanates are preferably used.

The polyisocyanate component used to prepare the prepolymer can also contain small amounts of higher-functionality polyisocyanates.

The preparation of the prepolymer is expediently carried out in the presence of catalysts, e.g. Organotin compounds or tertiary amines performed.

The polyurethane resin is converted into the aqueous phase, as described for the polyester resins, by neutralizing the acid group

Polyurethane resin with a basic neutralizing agent. Examples of basic neutralizing agents are those described above for neutralizing the polyester resins.

The coating composition according to the invention is preferably crosslinked when baked by reaction with a crosslinking component. Crosslinking components are familiar to the person skilled in the art. examples are Aminoplast resins, in particular melamine-formaldehyde resins; Phenolic resins; blocked polyisocyanates or transesterification crosslinking agents such as polyesters or polyurethane esters with hydroxyalkyl ester groups, acetoacetic acid or malonic acid alkyl ester derivatives, tris (alkoxycarbonylamino) triazine derivatives and mixtures of these crosslinking components which can give highly crosslinked coatings with or without the action of catalysts. Blocked polyisocyanates are preferred.

The blocked polyisocyanates contain on average more than one isocyanate group, preferably at least two isocyanate groups per molecule. They are said to be in the watery

Phase stable at about neutral to weakly basic pH, split when exposed to heat from about 100 ° C to 200 ° C and crosslink with the reactive hydroxyl and / or carboxyl groups present in the resin dressing.

Blocked polyisocyanates are obtained by reacting polyisocyanates with monofunctional compounds with active hydrogen.

Any organic di- and / or polyisocyanates with aliphatic, cycloaliphatic, araliphatic and / or aromatically bound free isocyanate groups are suitable as polyisocyanates, which can be used individually or in a mixture in a blocked form as crosslinking agents.

Polyisocyanates containing about 3 to 36, particularly preferably 8 to 15, carbon atoms are preferred. Examples of suitable diisocyanates are tolylene diisocyanate, diphenylmethane diisocyanate and in particular

Hexamethylene diisocyanate, tetramethylxylylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate and cyclohexane diisocyanate.

For example, "paint polyisocyanates" based on hexamethylene diisocyanate, isophorone diisocyanate and / or are very suitable

Dicyclohexylmethane diisocyanate, which are the known biuret, urethane, uretdione and / or isocyanurate group derivatives these diisocyanates.

Monofunctional compounds with active hydrogen that can be used to block the polyisocyanates are common. For example, CH-acidic compounds such as acetylacetone; CH-acidic esters such as alkyl acetoacetate,

Dialkyl malonate; (cyclo) aliphatic alcohols such as n-butanol, 2-ethylhexanol, cyclohexanone; Glycol ethers such as butyl glycol, butyl diglycol; Phenols such as cresol, tert-butylphenol; Diamino alcohols such as dimethylaminoethanol; Oximes such as butanone oxime, acetone oxime, cyclohexanone oxime; Lactams such as e-caprolactam or pyrrolidone-2; Imides; Hydroxyalkyl esters; Hydroxamic acids and their esters; Pyrazoles.

The polyisocyanates can be blocked within a molecule with the same or different blocking agents. Mixtures of polyisocyanates blocked the same or different can also be used.

The melamine-formaldehyde resins crosslink with the hydroxyl groups of the polyester resin to form ether groups. For example, these crosslinkers are triazines such as melamine or benzoguanamine, which are condensed by known technical processes in the presence of alcohols such as methanol, ethanol, propanol, butanol or hexanol with aldehydes, in particular formaldehyde. These are preferably methanol-etherified melamine resins such as Cymel 325, Cymel 327, Cymel 350, Cymel 370, Maprenal MF 927; Butanol or isobutanol etherified melamine resins such as e.g. Setamin US 138 or Maprenal MF 610; mixed etherified melamine resins, and in particular um

Hexamethylol melamine resins such as e.g. Cymel 301 or Cymel 303.

Because of the low content of organic solvent in component (A), it is advantageous to use component (A) as a conventional biocidal component to prevent infestation with microorganisms such as bacteria, yeasts, algae or

Add mushrooms, such as formaldehyde depot products, phenolic compounds, organic sulfur compounds or oxidizing agents. Commercially available anionically and / or non-ionically stabilized emulsifiers can also be used in quantities of up to 3% by weight, based on solid resin, for the production of component (A). In the preparation of components (A), the auxiliaries and additives customary in lacquer can also be added in the customary amounts, for example optical brighteners such as derivatives of stilbene, coumarin, 1,3-diphenylpyrazoline, naphthalimide, benzoxazole and thiophenbenzoxazole, customary catalysts, such as them are known to the person skilled in the art for the respective crosslinking systems; ethoxylated or propoxylated derivatives of substituted phenols or fatty alcohols with more than 10 C atoms as layer formers.

The aqueous pigmented component (B) contains one or more paste resins, pigments and / or fillers, neutralizing agents, water and expediently a biocidal component and, if appropriate, crosslinking agents and / or additives customary in lacquers, as described, for example, for component (A).

The layer formers can e.g. in amounts up to 10% by weight, based on the solids of the components, components (A) and / or (B) are added.

The addition can take place to the components (A) / or (B) or in the aqueous components (A) and / or (B) or in the coatable electrocoating bath. The layer formers are preferably added to the binders of components (A) and / or (B) before they are converted into the aqueous dispersion.

Suitable paste resins are polyester resins, polyurethane resins, polyacrylate resins and aminoplast resins, as are described in component (A). Polyester urethane resins are preferred.

A particularly preferred embodiment is, for example, OH group-containing urethanized oil-free polyesters with an acid number of 10 to 50 and a number average molecular weight (Mn) of 2,000 to 20,000. Such polyester urethane resins are obtained, for example, by reacting one or more polyester polyol (s) free of carboxyl groups and having an OH number of 35 to 200 and a number average molecular weight of 500 to 5000 with 2 to 30% by weight, based on the polyester polyol low molecular weight diols with a molecular weight of 60 to 350, some of the low molecular weight diols containing at least one acid group capable of forming anions, and with 0 to 6% by weight, based on the polyester polyol, of low molecular weight triols with a molecular weight of 60 to 350 one or more diisocyanates, in the ratio of the OH groups of polyester polyol, diol and triol to the NCO groups of the diisocyanate of more than 1.0 to 1.3. The polyester urethane resin is produced, for example, at

Temperatures from 20 to 150 ° C, preferably from 45 to 90 ° C, optionally with the addition of catalysts such as organotin compounds or tertiary amines. The polyaddition is carried out after rapid mixing of the components with good stirring in the melt or after dilution with dry solvents which do not react with the isocyanate group. It runs until practically everyone

Isocyanate groups are implemented. On the other hand, the reaction can also be carried out in stages. Depending on the use of diols or higher functional polyols, one or more hydroxyl groups are obtained at the chain end. In the step-by-step production, it is also possible to work in a different order. For example, the anionic-forming diol, such as dimethylolpropionic acid, in organic solvent which does not react with the isocyanate groups can first be reacted with one or more diisocyanates, followed by further reaction with polyester and low molecular weight diol and / or triol free of anion groups. If desired, the polyaddition can be terminated by monofunctional additives such as butanone oxime, dibutylamine or alcoholic solvents. The solvents which do not react with the isocyanate groups are intended to keep the reactants in a liquid state and to enable better temperature control during the reaction. Suitable solvents are, for example, dimethylformamide, dimethylacetamide, l-methyl-2-pyrrolidone, acetonitrile, tetrahydrofuran, dioxane,

Esters such as ethyl acetate, but also ketones such as acetone, fully etherified mono- or diglycols of ethylene glycol or propylene glycol, and with methoxy groups substituted ketones.

Before the polyester urethane resin is transferred into the aqueous phase, the aforementioned biocides, crosslinking agents and / or conventional lacquer additives are added to it. Then the transfer into the aqueous takes place

Phase as described for component (A).

Customary pigments, fillers, corrosion inhibitors and paint auxiliaries can be used for pigmenting the aqueous component (B), as long as they do not enter into interfering reactions with water in a weakly basic to neutral pH value and do not introduce water-soluble interfering foreign ions.

Suitable pigments are, for example, inorganic pigments, e.g. White pigments such as titanium dioxide, zinc sulfide, lithopone, lead carbonate, lead sulfate, tin oxide, antimony oxide; colored inorganic pigments such as chrome yellow, nickel titanium yellow,

Chrome orange, molybdate red, iron oxide red, mineral violet, ultramarine violet, ultramarine blue, cobalt blue, chrome oxide green, iron oxide black; colored organic pigments such as toluidine red, lithol red, perylene red, thioindigo red, quinacridone red, quinacridone violet, phthalocyanine blue, indanthrene blue, phthalocyanine green, carbon black, graphite; Corrosion inhibitors such as zinc chromate, strontium chromate, zinc phosphate,

Lead silicone chromate, barium etaborate and zinc borate.

Effect pigments such as aluminum bronzes, pearlescent pigments or interference pigments can also be used. For example, calcium carbonate, silicon dioxide, aluminum silicates, magnesium silicates, mica,

Barium sulfate, aluminum hydroxide and silicas can be used.

The aqueous pigmented component (B) can also be admixed with conventional auxiliaries, such as anti-foaming agents, dispersing aids and rheology control agents.

The aqueous pigmented component (B) is prepared in the usual manner, the A person skilled in the art by dispersing the pigments and auxiliaries in the paste resin. The composition of the ingredients for optimal dispersion is determined separately for each dispersing unit. Suitable dispersing units are, for example, stirring disc devices, three-roll mills, ball mills or, preferably, sand or pearl mills.

Components (A) and (B) are used for coating in a mixing ratio of 1: 1 to 4: 1, based on the weight of the respective aqueous components.

In the case of post-compensation in a running ATL bath, the two components are mixed with the bath material in the specified mixing ratio. For this purpose, both components can be added to the bath at the same time or in succession. The components are preferably premixed with part of the bath material in a conventional mixing device. Such a mixing element can be, for example, a stirred tank, a static mixer or a rotor / stator mixer. Components (A) and (B) can also be mixed beforehand in the desired ratio and used as a one-component material for post-compensation.

When an ATL bath is first prepared, component (A) is mixed with additional neutralizing agent in order to obtain the desired MEQ value of the ATL bath and, if appropriate, prediluted with water. Then component (B) is fed in in the manner described above and the mixture is adjusted to the desired final solid for the coating. Another

The first step is to present the required amount of water with the neutralizing agent and to supply components (A) and (B) in the manner described above.

During operation, the ATL bath has a solids content of 8 to 25% by weight, preferably 10 to 15% by weight, an MEQ value of 50 to 90, preferably 60 to 70 and an organic solvent content of less 0.3% by weight. The deposition is carried out by applying a DC voltage of 50 to 500 volts with a coating time of 0.5 to 5 minutes at a temperature of the ATL bath of 18 to 35 ° C.

The coating material is suitable for coating workpieces with an electrically conductive surface, in particular for priming and single-layer coating of household and electrical appliances, steel furniture, components, construction and agricultural machinery, automobile bodies and automotive accessories.

Examples

1. Preparation of an Aqueous, Crosslinker-Free, Pigment-Free Binder Component (AI)

To 57.65 parts by weight of a polyester resin with an acid number of 49 and a hydroxyl number of 60 (made from 26.17 parts by weight of neopentyl glycol, 5.43 parts by weight of trimethylolpropane, 10.83 parts by weight of isophthalic acid, 21.45 parts by weight of isodecanol and 36.12 parts by weight of trimellitic anhydride) a mixture of 2.55 parts by weight of dimethylethanolamine (50%) and 3 parts by weight of deionized water is added in a reaction vessel with stirrer, thermometer and reflux condenser, at 100 ° C. and stirred in for 10 minutes, then 0J5 parts by weight of a commercially available biocide are also added for 10 minutes homogeneously stirred. 36.65 parts by weight of fully demineralized water are added with stirring. The mixture is stirred at 80 ° C. for 90 minutes and then rapidly cooled to 25 ° C.

Key figures:

Solid 30 minutes 180 ° C 57%

MEQ-.Amin 29 milliequivalents amine / 100 g solid resin

Solvent content <0J% 2. Production of an aqueous crosslinking pigment-free binder component (A2)

To 47.75 parts by weight of a polyester resin with an acid number of 49 and a hydroxyl number of 60 (made from 26.17 parts by weight of neopentyl glycol, 5.43

Parts by weight of trimethylolpropane, 10.83 parts by weight of isophthalic acid, 21.45 parts by weight of isodecanol and 36.12 parts by weight of trimellitic anhydride) are stirred in a reaction vessel with stirrer, thermometer and reflux condenser, at 100 ° C. 0.12 part by weight of a commercially available nonionic emulsifier. 8.03 parts by weight of a solvent-free crosslinker (isocyanurate from

Hexamethylene diisocyanate, blocked with butanone oxime) are previously heated to 70 to 80 ° C, added to the mixture and stirred homogeneously for 15 minutes. A mixture of 1.38 parts by weight of diisopropanolamine (50%), 0.7 parts by weight of ammonia spirit and 2.60 parts by weight of completely deionized water is then added and the mixture is stirred in homogeneously for 10 minutes.

Then 0J5 parts by weight of a commercially available biocide are added and stirred in homogeneously for 10 minutes. 39.27 parts by weight of deionized water are added with stirring. The mixture is stirred at 80 ° C. for 90 minutes and then rapidly cooled to 25 ° C.

Key figures:

Solid 30 minutes 180 ° C 53%

MEQ-.Amin 32 milliequivalents amine / 100 g solid resin solvent content <0.1%

3. Production of an aqueous crosslinking, pigment-free binder component (A3)

90.60 kg of the aqueous binder component (AI) are in one

Dissolver mixer 9.40 kg of a melamine resin of the hexamethylol melamine resin type are added with stirring and the mixture is stirred at 40 ° C. for 30 minutes. Solid 30 minutes 180 ° C: 60.8%

MEQ amine: 24.6 milliequivalents amine / 100 g

Solid

4. Production of a solvent-free paste resin

453.5 g of a linear polyester of adipic acid and hexanediol with a hydroxyl number of 110 g together with 37.1 g of dimethylolpropionic acid are dissolved in 134 g of acetone at 50 ° C. in a reaction vessel with an internal thermometer and reflux condenser. 159.5 isophorone diisocyanate are added so that the reaction temperature of 70 ° C is not exceeded. The reaction temperature is kept until an NCO number of about 0.5% and a viscosity measured 60% in acetone solution of about 1200 mPa.s is reached. Then 10 g of butyl glycol are added in order to deactivate the remaining NCO groups. The mixture is then neutralized with 30.0 g of 50% dimethylethanolamine solution and an aqueous dispersion is prepared with 1450 g of water. The acetone is removed from the reaction mixture by distillation, so that a solvent-free aqueous polyurethane dispersion is obtained.

Key figures:

Solid 30 minutes 150 ° C: 30.1%

Acid number: 24.1 mg KOH / g MEQ amine: 26 milliequivalents amine / 100 g solid resin

5. Preparation of an aqueous pigmented component (B1)

To produce 100 kg of pigmented component (B), 56.85 kg of the paste resin are placed in a dissolver mixer and in the order given

Sprinkled in 21.20 kg of coarse carbon black and 2.12 kg of a furnace black and 19.83 aluminum hydrosilicate. The regrind created in this way is at 15 minutes Stirred at 40 ° C. After a swelling time of 12 hours, the millbase is dispersed on a Coball Mill under specified conditions.

Solid 30 minutes 180 ° C: 60.2% MEQ amine: 7.1 milliequivalents amine / 100 g

Solid

6. Preparation of an aqueous pigmented component (B2)

To produce 100 kg of the pigmented component (B2), 42.00 kg of the

Paste resin placed in a dissolver mixer and sprinkled in the order given 41.70 kg titanium dioxide, 7.00 kg aluminum hydrosilicate, 7.00 kg post-treated aluminum hydrosilicate, 1.80 kg silicon dioxide and 0.50 kg of a polybutylene with stirring. The regrind prepared in this way is stirred for 20 minutes at 50 to 60 ° C. and then dispersed on a Coball mill under specified conditions.

Solid 30 minutes 180 ° C: 70.1%

MEQ amine: 4.5 milliequivalents amine / 100 g solid

7. Production of electrocoating bath black crosslinking pigment-free aqueous binder component (A3) Aqueous pigmented component (Bl) Mixing ratio: component A3: component Bl = 3.5: 1

1669.65 g of completely demineralized water are initially introduced and 7.35 g of neutralizing agent (100% dimethylethanolamine) are added. 252 g of the pigment-free aqueous binder component (A3) are then slowly added with stirring or circulation. After 30 minutes of homogenization, 71 g of the aqueous pigmented component (B1) are added with stirring or circulation. After a homogenization time of about 1 hour, that is Electrodeposition bath ready for coating.

Bath values:

pH: 8.6

Conductivity: 1234 μS / cm

Solid 30 minutes 180 ° C: 9.8%

MEQ amine: 62.9 milliequivalents amine / 100 g

Solid

8. Production of electro dip lacquer bath gray

Crosslinker-containing pigment-free aqueous binder component (A2)

Aqueous pigmented component (B2)

Mixing ratio: component A2: component B2 = 2.0: 1

First, 1632 g of completely demineralized water are introduced and 14.6 g of neutralizing agent (50% diisopropanolamine) are added. 237.4 g of the pigment-free aqueous binder component (A2) are then slowly added with stirring or circulation. After 30 minutes of homogenization, 116 g of the aqueous pigmented component (B2) are added with stirring or circulation. After a homogenization time of about 1 hour, the electro-immersion bath is ready for coating.

Bath values: pH: 8.1

Conductivity: 1094 xS / cm

Solid 30 minutes 180 ° C: 10.4%

MEQ amine: 47.7 milliequivalents amine / 100 g

Solid

Claims

Claims:

1. A method for anodic electrocoating, in which the coating agent consumed in an anodic electrocoating bath is compensated for by a neutralized anodic refill material, characterized in that the refill material consists of

A) a pigment-free aqueous binder component with a

Solids content of 40 to 70 wt .-%, an MEQ value of 15 to 40 and an organic solvent content of <0.5 wt .-% and

B) a pigment-containing aqueous paste resin component with a

Solids content of 60 to 75% by weight, an MEQ value of 5 to 15 and an organic solvent content of <1.0% by weight,

wherein A) to B) are present in a weight ratio of 1: 1 to 4: 1 and the mixture of A) and B) has a solids content of 45 to 73% by weight, one

Solvent content of ≤ 0.75 wt .-% and an MEQ value that is 50 to 70% lower than the MEQ value of the electro-dip.

2. The method according to claim 1, characterized in that component A) and / or component B) contains one or more conventional biocidal agents.

3. The method according to Anspmch 1 or 2, characterized in that component A) contains one or more film-forming binders, emulsifiers, layering agents and / or customary auxiliaries and, if necessary, one or more crosslinking agents.

4. The method according to any one of claims 1 to 3, characterized in that the Component B) contains one or more paste resins, pigments and / or fillers, and / or auxiliaries customary in paint and, if necessary, one or more crosslinking agents.

5. The method according to any one of claims 1 to 4, characterized in that it is carried out for coating industrial goods or motor vehicle bodies or their parts.

6. The method according to any one of claims 1 to 5, characterized in that it is carried out without electrodialysis of the electrodeposition bath.